You don't actually "pop" them. Where the seam of the two pieces intersect, there's a vertical seam - generally 3-4 stitches from the intersecting seam to the raw edge of the seam allowance. I just very gently use my seam ripper to pick those 3-4 stitches out on both vertical stitches to the seam that crosses it. Do that on both sides then "smush" (technical Eleanor Burns term) them open.